1. Field of the Invention
The present invention relates to a communication system comprising a plurality of communication apparatuses that transmit data and a plurality of distribution apparatuses that receive and distribute data being sent from each communication apparatus, the communication system allowing each distribution apparatus to distribute data toward each communication apparatus based on a request. Especially, the present invention relates to a distribution apparatus that implements reducing a traffic for data transmission for sending data to each communication apparatus and reducing a memory capacity of a storage means for temporally storing data received from each communication apparatus by a distribution apparatus, communication system comprising such a distribution apparatus and a communication method utilizing such a distribution apparatus.
2. Description of Related Art
It is recently known in several fields to utilize a system having many communication apparatuses, in which each communication apparatus is provided a certain function and connected with other communication apparatuses in order to perform variable operations through data exchange between many communication apparatuses. For example, it is known in a field of local area network (LAN) adapting for car to utilize electronic control units (ECUs) as the communication apparatuses, to make each ECU perform a certain operation and to exchange data between the ECUs, in order to provide various functions as a system.
A number and a type are increased of the communication apparatuses connected to a communication medium in a system, proportionally to a specializing degree of the function provided to each communication apparatus, as well as an increasing degree of the functions performed by the system. Furthermore, the system is expected to perform much more various functions. Thus, each communication apparatus is required to share data and to interact with other communication apparatuses. Then, it results in an increase of exchanged data amount.
To accommodate the increase of exchanged data amount, communication apparatuses of the system is generally classified into some groups, and then each group is connected to each of communication lines, respectively. Furthermore, it is thought to focus on data type treated by the groups of communication apparatus, and then to connect each group to each of communication lines respectively having different communication speed. In such a configuration, a communication line is connected with another communication line, by a gateway apparatus that relays data transmission.
Japanese Patent Application Laid-Open No. 2005-159568 discloses that: ECUs in a field of LAN adapting for car are classified into some groups; each group is connected to each of communication lines; the communication lines are connected to each other by a gateway apparatus; priority information is added to the received and the sent data to recognize data priority; the data priority is recognized through the priority information and the data having high priority is preferentially transmitted when the gateway apparatus performs data transmission between different communication lines, to prevent a transmission delay of data having high priority even when the communication lines take increased duty for data transmission.